The present invention relates to a surveying system which is used for irradiating laser beam and scanning, for detecting a reflecting object, performing marking, position setting and level setting, and for measuring the distance up to the reflecting object.
In recent years, a surveying system for irradiating laser beam and scanning has been introduced in the field of civil engineering and architectural engineering in order to set a reference for height or to measure the distance up to an object point.
A surveying system has been known in the past, in which laser beam is rotated around a vertical line, a horizontal reference plane is formed by laser beam, or a horizontal reference line of a given height is formed by scanning laser beam on wall surface, irradiation light beam is irradiated toward a reflecting object, the reflecting object is detected according to the light beam reflected from the reflecting object, and the distance up to the reflecting object is measured.
Description will be given on a case where marking, position setting and level setting are carried out using such a surveying system. Laser beam irradiated from a light source unit of the surveying system is divided into visible light and invisible light
On rotational laser level using visible light, irradiation position of laser irradiation beam (hereinafter referred as "irradiation beam") is visually confirmed according to reflection from an object, which has a reflecting portion ("reflecting object"). Further, in order to improve visual confirmation, a light receiving element having high sensitivity is provided on the rotational laser level so that laser beam reflected from the reflecting object at the irradiation position of laser beam can be received and detected, and laser beam is scanned reciprocatively on and around the position where light is received.
On rotational laser level using invisible light, a photoelectric conversion element having high sensitivity is provided on the object so that irradiation status of laser beam to the object is electrically displayed.
The reflecting object in the former case as described above is advantageous in that the irradiation position of laser beam can be visually confirmed and working efficiency is high, whereas output of laser beam is limited to ensure safety for operators, and this results in difficulty for visual confirmation at long distance. As described above, apparent luminance is increased by detecting the light reflected from the reflecting object and by reciprocatively scanning on and around the reflecting object. However, visual confirmation is still difficult at a place under direct sunlight.
In the object in the latter case, light velocity traversing the photoelectric conversion element increases as the distance from the object becomes longer. Thus, photoelectric conversion element of the object or electric circuit must have higher response speed and this leads to problems in power consumption and cost reduction.
As a conventional type surveying system for measuring the distance to a reflecting object based on laser beam reflected from the reflecting object, a surveying system is disclosed in Japanese Paten Publication Laid-Open No.63-259411. This system is provided with a wave transmitter and a wave receiver, and a laser reference plane is formed by rotating laser light beam in order to detect two reflecting objects, which are arranged with a spacing between them. The distance from the surveying system to the reflecting object is measured by pulse spacing between two pulses generated when laser beams reflected from the two reflecting objects are received. Also, it is known from this patent publication that laser beam is modulated, and that the distance is measured by measuring phase difference between a modulation signal and a signal obtained by demodulating reflected laser energy. Further, in Japanese Patent Publication Laid-Open No.4-313013, for instance, a phase difference type light wave range finder is incorporated in a surveying system which forms a laser reference plane by rotating laser beam. Also, as disclosed in Japanese Patent Publication Laid-Open No. 57-119274, a surveying system is known, which alternately issues modulated irradiation light beam for measuring distance and light beam for data transmission.
However, it is disadvantageous in decreasing working efficiency and measuring efficiency that modulated irradiation light beam for measuring distance and light beam for data transmission are respectively irradiated to the reflecting object by time sharing.